The first 3 of Sagan's 4 criteria for life, as gleaned from Galileo's Earth flyby, are all related to porphyrins through the action of chlorophyll. Chlorophyll and photosynthesis are responsible for the spectral colors of plant-covered continents, for the oxygen content of the atmosphere and for its methane balance. Galileo didn't detect porphyrins during its flyby of the Moon, but they were there in quantities too small to see.
Right: Porphyrin molecules seem fully capable of biological wizardry on Earth. Put an iron atom in a porphyrin and the closely related oxygen-carrying blood molecule, hemoglobin, results. Put a magnesium atom in a porphyrin and the closely-related light-harvesting molecule, chlorophyll, is made. Put lunar soil specimen, 12023, into the lab for chemical analysis, and porphyrin shows up on the moon.
Here on Earth porphyrin organic compounds are useful biomarkers. For example, petroleum hunters look for porphyrins as markers of oil deposits and thermal maturity. They can be detected remotely without extracting organic matter to reveal oil shales and source rock that came from the decay of green plants.
Does the presence of porphyrins mean that there is or has been life on the Moon?
Not at all. The 1969 discovery of lunar porphyrins probably says less about the chances for biochemistry there, than about how common their generation may be elsewhere in the universe. In 1978 Simionescu et al. were able to produce porphyrins under laboratory conditions similar to those of primaeval Earth, before the genesis of life. They summarized the results in the journal Origins of Life:
"Experiments with gas mixtures intended to simulate the primaeval atmosphere of the Earth yielded many biologically important chemicals. Investigations into the synthesis of porphyrin-like compounds from methane, ammonia and water vapour were carried out by using high frequency discharges. Microanalyses
Contact: Linda Porter
NASA/Marshall Space Flight Center--Space Sciences Laboratory